In the question four alternatives are given for the underlined word in the sentence.
Choose the alternative which best expresses the opposite meaning of the word.
“Well, what if it is? You are not afraid of anything, you know,” returned the boy, looking wicked.

The correct answer is Righteous.

Step 1: Understand the meaning of the given word
In the provided sentence, the underlined word is wicked.
The word "wicked" refers to something or someone that is morally wrong, evil, bad, or mischievous in nature.

Step 2: Analyze the given options
• Clean: Free from dirt, marks, or stains; morally pure, but usually refers to cleanliness or lack of guilt.
• Evil: Profoundly immoral and wicked. This is a synonym of "wicked", not an opposite.
• Righteous: Morally right, virtuous, or acting in accordance with divine or moral law. This is the exact opposite (antonym) of "wicked".
• Improper: Not in accordance with accepted standards or rules; dishonest or unseemly.

Step 3: Conclusion
Since we need to find the word that best expresses the opposite meaning (antonym) of "wicked", the word Righteous is the correct choice.